1. Field of the Invention
Embodiments of the present invention generally relate to a method of etching. More specifically, the invention relates to a method for etching having a controlled distribution of process results.
2. Background
In manufacture of integrated circuits, precise control of various process parameters is required for achieving consistent results within a substrate, as well as the results that are reproducible from substrate to substrate. During processing, changes in the temperature and temperature gradients across the substrate may be detrimental to material deposition, etch rate, step coverage, feature taper angles, and other parameters of semiconductor devices. As such, generation of the pre-determined pattern of temperature distribution across the substrate is one of critical requirements for achieving high yield.
The 2003 edition of the International Technology Roadmap for Semiconductors states that reduction in the transistor gate critical dimension (CD) will be a key challenge for etch technology in the future. Therefore, much work has been done to study the influence of gate etch process parameters on the ability to control CD's, since the gate CD contributes significantly to the ultimate performance of a device. Several different strategies for gate CD control have been published, including photoresist trimming and control of the gate hard mask etch chemistry. The former approach reduces the photoresist dimension below what is possible lithographically by lateral etching of the photoresist, while the latter approach relies on etch by-products redeposited on the sidewalls during the hard mask etch to passivate and control the amount of lateral etching relative to vertical etching. Sidewall passivation by etch by-products is not limited only to the hard mask etch step, but also occurs during the gate main etch, soft landing, and over etch steps.
The rate of this redeposition of etch by-products is expected to follow both the gas phase concentration of by-products and the sticking coefficient of those by-products. Sticking coefficients have been used in gas-surface reaction mechanisms to describe the probability of an incident gas phase species adsorbing to a surface, and they are typically approximated as the ratio of the number of species that are reactively adsorbed on a surface to the total number of incident species.
However, conventional substrate pedestals have insufficient means for controlling substrate temperature distribution across the diameter of the substrate. The inability to control substrate temperature uniformity has an adverse effect on process uniformity both within a single substrate and between substrates, device yield and overall quality of processed substrates.
Therefore, there is a need in the art for an improved method for etching a substrate.